HOPE (AP) — More than one-third of Arkansas is experiencing drought conditions, raising concerns among farmers about fires starting in hay fields.

The latest U.S. Drought Monitor shows far southern Arkansas is in extreme drought, while parts just north are in either severe or moderate drought. As such, the Arkansas Forestry Commission says the wildfire danger in the state is either high or moderate, with dozens of counties under burn bans.

Hay bale fires can be sparked when mower blades strike rocks. Hay bales can also spontaneously combust, under the right conditions.

“There are several factors that make hay fires difficult to extinguish,” said Jon Barry, an extension forester for the University of Arkansas System Division of Agriculture. Barry is also a volunteer firefighter in southwestern Arkansas.

Round bales of burning hay are difficult to extinguish because they’re “tightly compressed,” he said, comparing it to a roll of paper.

“It is a smoldering fire that burns up into the bale. The bale has to be taken apart to get to the fire so it can be put out, and all of it has to be put out or it will flare up again,” he said.

If the bale is out in a hay field, “the most effective approach is to get the farmer to tear the bale apart with his tractor,” Barry said. “If the terrain is flat, sometimes we just push the bale along and unroll it.”

If it’s burning and has to be hosed down, the bale is ruined anyway, so there’s no reason not to unroll it or tear it apart.

“Grass is a tough plant and that gives round hay bales a distinct tough grain pattern almost like wood grain,” Barry said. “When we are trying to get into the bale to find the smoldering area, we have to work across the grain, and that’s hard work.”

Square bales tend to burn more quickly and more intensely than round ones.

Hay fires can also be started by fermentation, which occurs when hay is baled when is too moist.

Moisture monitoring is important to ensure high-quality hay. Microbes in the hay will flourish if it’s too damp, which can cause heat, said Dirk Philipp, assistant professor for the Division of Agriculture.

Fermenting hay can heat up to 180 degrees or higher, which brings the risk of spontaneous combustion, Philipp said.